Method of forming amalgam films on amalgam alloys



Patented Jan. 17, 1939 UNHTED STATES PATENT OFFICE METHOD OF? FORMING AMALGAM FILMS ON AMALGAM ALLOYS No Drawing. Application June 3, 1937, Serial No. 146,288

6 Claims.

This invention relates in general to dental alloys and more particularly to alloys which are mixed with mercury or the like. to produce a plastic amalgam which will harden and solidify at ordinary temperatures. Such alloys are generally prepared for use by the dentist in the form of chips or granules, and the plastic amalgam is generally made by the dentist by triturating or mixing the alloy chips or granules and mercury, usually with a mortar and pestle.

The surfaces of the chips or granules frequently become coated with a film of tarnish, and in order to form a satisfactory mixture of the mercury and alloy, this film of tarnish must be substantially reduced or removed. The trituration of the chips or granules reduces or removes the tarnish to some degree, but during the trituration in an effort to obtain the desired union of the mercury with the alloy, the alloy particles are frequently broken down to such an extent as to detrimentally affect the desired properties of the alloy. For example, it is known that the volume changes upon hardening of the amalgam, the adaptation of the amalgam to the walls of a tooth cavity, as well as the grain structure of the amalgam, depend to a large extent upon the size and uniformity of size of. the alloy particles at the time of mixing thereof with the mercury.

Therefore, an important object of our invention is to provide particles of alloy of the general character described which shall have substantially non-tarnishable surfaces whereby the amount of trituration required for mixing of the alloy particles with the mercury shall be reduced so that the mixture can be effected in less time than heretofore possible and the possibility ofexcessive breaking down of the particles shall be minimlzed.

Another object is to provide an amalgam alloy of the character described, the particles of which as supplied to the dentist for use, shall be coated with a thin film of amalgam so that the surfaces of the particles shall be substantially non-tarnishable whereby little or no trituration shall be required for preparing a plastic amalgam for use in, for example, filling a tooth cavity.

Further objects are to provide a novel and improved method of applying a substantially non-tarnishable coating to particles of amalgam alloy, and thus to provide a novel and improved method of applying a thin film of amalgam upon the surfaces of the alloy particles.

Other objects, advantages and results of the invention will appear from the following description.

As above indicated, our invention is applicable to many different alloys, but the more common dental amalgam alloy usually contains not less than 65% silver, not less than 25% tin, not more than 6% copper, and not more than 2% zinc. 5 lhe invention is also applicable to alloy particles of any size, but is most satisfactory with alloy particles that do not require reduction in size during trituration, for example particles having dimensions ranging between 10 and 200 microns. 10

One method of carrying out our invention comprises the immersion of the alloy particles in a solution of an alkali or alkaline earth double mercury cyanide, for example five grams of mercury metal in the form of a cyanide and ten 15 grams of potassium cyanide are dissolved in 500 cubic centimeters of Water, and grams of the alloy particles are immersed in the solution. Slight heating of the solution to 100 or F. is desirable for accelerating the reaction although 0 heating is not necessary. H

The mercury cyanide and the potassium cyanide combine to form potassium mercury cyanide which is the reactive agent in the solution. Instead of potassium cyanide we can use any other 25 alkali double cyanide or any water soluble alkaline earth double cyanide, for example the potassium cyanide may be replaced by sodium cyanide, barium cyanide, calciurn cyanide, etc.

During the reaction in the solution an ex- 30 change takes place between the mercury and one or more of the metals contained in the alloy, thus forming a film of amalgam on the surfaces of the alloy particles. In order to prevent the formation of insoluble metal cyanides which 35 would be difficult to separate from the alloy particles, an excess of alkali cyanide is added to permit the formation of soluble double metal cyanides.

We have found also that the addition of strong 40 alkalies to the solution accelerates or promotes the reaction due to the fact that hydrolysis of the cyanide is retarded with consequent retarding of the decomposition of the cyanide; for example, 10 cubic centimeters of a 10% solution of 45 caustic soda or caustic potassium may be added to the solution to promote the reaction.

After the reaction has been completed, that is, after the formation of amalgam on the surfaces of the alloy particles has ceased, the alloy par- 50 ticles are allowed to settle and all traces of the solution. are removed by thorough washing.

The alloy particles thus produced have cores substantially free from mercury and surface films of amalgam which are practically wholly 55 resistant to tarnish, and the mercury used in preparing plastic amalgam from the particles therefore will quickly unite with the particles. Therefore, little or no trituration is necessary; for example with 1.5 grams of finely comminuted alloy in coated form according to the invention and 2.7 grams of mercury, it is possible to complete mixture of the amalgam in from ten to fifteen seconds with stirring at the rate of 200 R. P. M. This is in contrast to one minute of trituration required for proper mixing of the same amount of mercury and the same amount of alloy of the same particle size without the amalgain surface films on the particles. This slight trituration results not only in the saving of time but also reduces the possibility of the particles being excessively broken down.

In many cases trituration by means of mortar and pestle can be eliminated entirely because amalgamation can be obtained by shaking in a test tube the new alloy particles and the mercury until the mix balls up, and then kneading the mix in the hand or suitable apparatus until it has the proper plasticity. With this method of amalgamation the particles of alloy are not broken down at all and the properties of the amalgam will bear a direct relationship to the size and shape of the initial alloy particles.

Furthermore, the color of the amalgam iSi greatly improved due to the absence of surface tarnish on the initial particles. Any tarnish which may have been acquired by the particles during manufacture is removed during the coating process of the invention, and tarnish of the coated alloy particles is practically impossible.

While the above described method has been found to be satisfactory, other methods may be utilized. Other compounds of mercury such as chlorides, sulphates, nitrates and the like may be used. However, as these salts have a tendency to hydrolize in the water, the addition of an acid is necessary, preferably the addition of an. acid corresponding. to the salt, for example nitric acid in the case of mercury nitrate. This modified method comprising the use of chlorides, sulphates and nitrates of mercury in an acid solution is not without disadvantages in that precipitates of salts occur when the alloy is added to a solution. For instance, calomel is precipitated where mercury chloride is used in the solution. These precipitates must be dissolved with acids, thus causing inconvenience and possible harm to the alloy particles.

However, we have found that better results can be obtained with this modified method by the use of an acidified alcoholic solution. As a specific example; we may prepare a solution of 500 cubic centimeters of alcohol, ten grams of mercury in the form of a chloride and ten cubic centimeters of hydrochloric acid, and add one hundred grams of the alloy particles to the solution. This kind of solution is quite satisfactory as only a slight precipitate of a salt is formed which can be removed as above described.

While we have described several forms of our invention it should be understood that this is primarily for explaining the principles of the in.- vention and that modifications and changes may be made in the alloy particles and the method without departing from the spirit or scope of the invention.

Having thus described our invention, what we claim is:

1. The method of forming films of amalgam on the surface of alloy particles for amalgams, consisting in immersing the particles in a solution containing a soluble double cyanide of mercury.

2. The method set forth in claim 1 with the addition of an accelerator in. the form of a strong alkali.

3. The method of forming films of amalgam on the surfaces of alloy particles for amalgams, consisting in immersing the particles in a solution containing a soluble alkaline earth mercury cyanide.

4. The method of forming films of amalgam on the surfaces of alloy particles for amalgams, con.- sisting in immersing the particles in an acidified alcoholic solution of a soluble mercury salt and thereafter removing. any precipitate from the solution.

5. The method of forming films of amalgam on alloy particles to be used for amalgams, said method consisting in treating the alloy particles with a solution containing an alkali mercury cyanide.

6. The method of forming a film of amalgam on the surface of an alloy to be used in forming amalgams, said method consisting in treating the surface of the alloy with a solution containing potassium mercuric cyanide KARL SCHUIWPELT. EDWARD O. LIEBIG. 

